The gain and the sensitivity of an optical receiver in an optical communication system are very important characteristics, for the optimization of the transmission performance depends on a simultaneous increase of these two characteristics. A conventional single-stage TIA, as shown in FIG. 1, contains a simple circuit structure 100 and has good stability. Its major components include a photodiode 101 and a basic operational amplifier 102. The overall gain and the bandwidth of an amplifier are heavily dependent on the output impedance of the amplifier. Therefore, this kind of single-stage TIAs has neither a high feed-back resistance RF nor a high sensitivity due to its low voltage gain.
Generally speaking, a multi-stage TIA 200 shown in FIG. 2 can be adopted to increase the voltage gain. This kind of multi-stage TIAs comprises multiple cascaded single-stage amplifiers 201-203 to achieve a high feed-back impedance RF and a high sensitivity. Though a high voltage gain is obtained on this multi-stage structure, the phase margin is hard to control. Especially for applications with a high dynamic range, the stability of automatic gain control (AGC) is questionable. Moreover, the large power consumption resulted from the multi-stage structure will greatly increase the difficulty in designing a high-bandwidth system.
If the equivalent output impedance of a TIA with respect to the ground is increased, its voltage gain can be greatly enhanced. Then, the above problems related to the conventional TIAs will likely be resolved.